Site-specific administration of antisense oligonucleotides using biodegradable polymer microspheres provides sustained delivery and improved subcellular biodistribution in the neostriatum of the rat brain

Antisense oligonucleotides (ODNs) are being increasingly used in the centra l nervous system as biological tools, as drug-target validation agents and as potential therapeutic agents. Although the local delivery of naked ODNs to the brain can result in the desired biological effects, the duration of efficacy is relatively short lived due to the combined effects of rapid ODN degradation and elimination half-lives in vivo. In this study, we have exa mined the use of biodegradable polymer microspheres as a site-specific deli very system for targeting ODNs to the neostriatum of the rat brain. Model p hosphorothioate backbone-modified ODNs were entrapped within poly(D,L-lacti de-co-glycolide) (PLAGA) microspheres using a double emulsion-deposition me thod and the formulations characterised in terms of particle size, surface morphology, percent encapsulation efficiency, ODN loading and in vitro rele ase profiles. For in vivo evaluation, PLAGA microspheres containing fluores cently-labelled ODNs were stereo-taxically administered to the neostriatum of the rat brain and biodistribution of ODNs monitored after 48 h. Administ ration of free fluorescently-labelled ODNs to the neostriatum resulted in a punctate cellular distribution of ODNs after 24 h with little or no ODN re maining in the neostriatum after 48 h. In comparison, fluorescently-labelle d ODNs delivered using polymer microspheres were intensely visible in cells after 48 h post-administration and the fluorescence appeared to be diffuse covering both cytosolic and nuclear regions. Dual-label immunohistochemica l analyses suggested that ODNs were mainly distributed to neuronal cells. T hese data indicate that site-specific administration of of ODNs using biode gradable polymer micropheres will not only provide sustained delivery of nu cleic acids but can also improve the cellular distribution of ODNs to brain cells. Sustained or controlled-release biodegradable polymer formulations, therefore, represent an attractive strategy fur improved local delivery of ODNs to the CNS.